BefA, a microbiota-secreted membrane disrupter, disseminates to the pancreas and increases β cell mass

A bacterial membrane-disrupting protein stimulates animal metamorphosis

Diverse marine animals undergo a metamorphic larval-to-juvenile transition in response to surface-bound bacteria. Although this host-microbe interaction is critical to establishing and maintaining marine animal populations, the functional activity of bacterial products and how they activate the host's metamorphosis program has not yet been defined for any animal. The marine bacterium Pseudoalteromonas luteoviolacea stimulates the metamorphosis of a tubeworm called Hydroides elegans by producing a molecular syringe called metamorphosis-associated contractile structures (MACs). MACs stimulate metamorphosis by injecting a protein effector termed metamorphosis-inducing factor 1 (Mif1) into tubeworm larvae. Here, we show that MACs bind to tubeworm cilia and form visible pores on the cilia membrane surface, which are smaller and less numerous in the absence of Mif1. In vitro, Mif1 associates with eukaryotic lipid membranes and possesses phospholipase activity. MACs can also deliver Mif1 to human cell lines and cause parallel phenotypes, including cell surface binding, membrane disruption, calcium flux, and mitogen-activated protein kinase activation. Finally, MACs can also stimulate metamorphosis by delivering two unrelated membrane-disrupting proteins, MLKL and RegIIIɑ. Our findings demonstrate that membrane disruption by MACs and Mif1 is necessary for Hydroides metamorphosis, connecting the activity of a bacterial protein effector to the developmental transition of a marine animal.

IMPORTANCE

This research describes a mechanism wherein a bacterium prompts the metamorphic development of an animal from larva to juvenile form by injecting a protein that disrupts membranes in the larval cilia. Specifically, results show that a bacterial contractile injection system and the protein effector it injects form pores in larval cilia, influencing critical signaling pathways like mitogen-activated protein kinase and calcium flux, ultimately driving animal metamorphosis. This discovery sheds light on how a bacterial protein effector exerts its activity through membrane disruption, a phenomenon observed in various bacterial toxins affecting cellular functions, and elicits a developmental response. This work reveals a potential strategy used by marine organisms to respond to microbial cues, which could inform efforts in coral reef restoration and biofouling prevention. The study's insights into metamorphosis-associated contractile structures' delivery of protein effectors to specific anatomical locations highlight prospects for future biomedical and environmental applications.

BefA protein alleviates progression of non-alcoholic fatty liver disease by modulating the AMPK signaling pathway through the gut-liver axis

Non-alcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver diseases worldwide, necessitating urgent novel oral treatments. In this study, β-cell expansion factor A (BefA) was evaluated in a murine NAFLD model induced by high-fat diet (HFD). Our results revealed that BefA significantly reduced body weight (36.58 ± 1.55 g vs. 42.30 ± 1.96 g, p < 0.01), fat mass-to-body weight ratio (0.023 ± 0.019 vs. 0.300 ± 0.019, p < 0.05), liver weight (1.90 ± 0.07 g vs. 2.31 ± 0.21 g, p < 0.05), and liver function parameters (ALT, AST, ALP levels reduced, p < 0.05). Notably, BefA reversed the pathological features of NAFLD, decreasing hepatic steatosis score from 3.67 ± 0.47 to 1.67 ± 0.47 (p < 0.01). Mechanistically, BefA activated the AMPK signaling pathway, resulting in the suppression of lipogenic gene transcription (ACC, FASN, SREBP-1c) and the enhancement of fatty acid oxidation (CPT-1, PPAR-α). However, AMPK inhibitor and broad-spectrum antibiotics significantly attenuated the benefits observed with BefA treatment, increasing body weight, fat-to-body weight ratio, and liver weight (p < 0.05). Similar detrimental effects were also observed in liver function indices and histopathological characteristics. These findings underscore the pivotal role of both gut microbiota modulation and AMPK signaling in BefA's therapeutic efficacy, making it a promising multitargeted approach for NAFLD treatment.

Inter-kingdom communication and the sympoietic way of life

Organisms are now seen as holobionts, consortia of several species that interact metabolically such that they sustain and scaffold each other's existence and propagation. Sympoiesis, the development of the symbiotic relationships that form holobionts, is critical for our understanding the origins and maintenance of biodiversity. Rather than being the read-out of a single genome, development has been found to be sympoietic, based on multigenomic interactions between zygote-derived cells and symbiotic microbes. These symbiotic and sympoietic interactions are predicated on the ability of cells from different kingdoms of life (e.g., bacteria and animals) to communicate with one another and to have their chemical signals interpreted in a manner that facilitates development. Sympoiesis, the creation of an entity by the interactions of other entities, is commonly seen in embryogenesis (e.g., the creation of lenses and retinas through the interaction of brain and epidermal compartments). In holobiont sympoiesis, interactions between partners of different domains of life interact to form organs and biofilms, wherein each of these domains acts as the environment for the other. If evolution is forged by changes in development, and if symbionts are routinely involved in our development, then changes in sympoiesis can constitute an important factor in evolution.

Human-gut bacterial protein-protein interactions: understudied but impactful to human health

The human gut microbiome is associated with a wide range of diseases; yet, the mechanisms these microbes use to influence human health are not fully understood. Protein-protein interactions (PPIs) are increasingly identified as a potential mechanism by which gut microbiota influence their human hosts. Similar to some PPIs observed in pathogens, many disease-relevant human-gut bacterial PPIs function by interacting with components of the immune system or the gut barrier. Here, we highlight recent advances in these two areas. It is our opinion that there is a vastly unexplored network of human-gut bacterial PPIs that contribute to the prevention or pathogenesis of various diseases and that future research is warranted to expand PPI discovery.

The buzz within: the role of the gut microbiome in honeybee social behavior

Gut symbionts influence the physiology and behavior of their host, but the extent to which these effects scale to social behaviors is an emerging area of research. The use of the western honeybee (Apis mellifera) as a model enables researchers to investigate the gut microbiome and behavior at several levels of social organization. Insight into gut microbial effects at the societal level is critical for our understanding of how involved microbial symbionts are in host biology. In this Commentary, we discuss recent findings in honeybee gut microbiome research and synthesize these with knowledge of the physiology and behavior of other model organisms to hypothesize how host-microbe interactions at the individual level could shape societal dynamics and evolution.

Out of destruction comes new growth: Pore-forming antimicrobials make pancreas grow

Gut-residing bacteria are known to regulate the physiologies of distal organs. However, the mechanism behind the long-distance communication between gut microbes and distal organs remains unknown. In this issue of Cell Metabolism, two studies show that β cell expansion in the pancreas depends on bacterially induced antimicrobials produced in the gut.